The present invention relates to a solid state image sensor, and more particularly, to a linear solid state image sensor in which photo-responsive elements that optically read an image on an original, for example, are disposed in linearly.
Image processing apparatus such as facsimile apparatus and digital copy machines and the like have linear solid state image sensors as the image input devices for example. A contact type image sensor is configured so that the surface of the sensor is in close contact with the original, and therefore do not require an optical system for image focusing. This contact type image sensor has the characteristic of being able to read images on an original at full size. Of the various types of the contact type image sensor, the completely contact type image sensor does not require a gradient index lens placed between the original and a photo-responsive element array (hereinafter termed an element array) to lead the light, and the element array can be in direct contact with the original. Accordingly, this completely contact type image sensor has the advantage in which an entrance mechanism to lead the light reflected by an original to the element array can be made smaller.
Linear solid state image sensor (such as disclosed in Japanese Patent Laid Open No. 288668-1986) that can read images on an original at full size have been conventionally used. This solid state image sensor has a bi-directional shift register of which read out direction can be selected in one direction. Because of this bi-directional shift register, it is possible successively to read signal output from all photo-responsive elements and it is not necessary to rearrange the signals and also, it is possible to read an image of large area at high speed.
In addition, Japanese Patent Laid Open No. 253972-2986, discloses a solid state image sensor comprising a pair of sensor elements. In this solid-state image sensor, the wiring drawn from the bonding terminal of one pair of sensor elements to a board of the solid-state image sensor is disposed with mirror symmetry. Whereby, it is possible to have a high S/N ratio. Moreover, Japanese Patent Laid Open No. 231757-1986 discloses a solid-state image sensor in which a plural number of chips are disposed. In this solid-state image sensor, when these chips are adhered, the disposition is such that the adhesion surface forms an angle which is not perpendicular to the sensor surface. Whereby, there is an outlet for the adhesive to escape and random light reflection from the contact portion is reduced. Such a solid-state image sensor is disclosed in Japanese Patent Laid Open No. 234562-1986. Furthermore, Japanese Patent Laid Open No. 131860-1983, Japanese Patent Laid Open No. 97267-1984, Japanese Patent Laid Open No. 86963-1985 and the Electronic Information & Communications Association Technical Report ED-161 disclose a solid-state image sensor of which two chips is connected so as to form a linear sensor. In each of these disclosures is described a signal compensation method for the connector portion of the chips.
In particular, the solid-state image sensors disclosed in Japanese Patent Laid Open No. 28868-1986 and Japanese Patent Laid Open No. 253972-1896 use a bi-directional shift register that is selective in one direction. In this solid-state image sensor, it is necessary to enable data transmission at the contact portion of the two chips. Normally, the shift register has wiring for power supply, wiring for control signals and wiring for data input. In the entirety of a solid-state image sensor, in addition to this wiring, there is also power supply wiring for full-size sensors and wiring for image signal output. However, in the already mentioned prior art, not sufficient attention has been paid for the various influences that these wiring have. Taking out wires from the unit by wire bonding or the like and the existence of wiring pads therefor increase the number of manufacturing processes and the substrate area necessary. Whereby, when the completely contact type of full-size image sensor is designed, it becomes more difficult to make the unit compact and to reduce the price.
The solid-state image sensors disclosed in Japanese Patent Laid Open No. 231757 and No. 234562-1986 have elements such as a thin-film transistor and a photo-responsive element formed in the vicinity of a chip contact portion. However, in this case, there is no consideration for the possibility of damage to the element at the chip cutoff portion. When the two chips are connected, the connection surface is formed by cutting off that contact portion. There is no consideration for the influence of mechanical stress to which the elements are subject and destruction due to the mechanical stress on the characteristics of individual elements.
FIG. 1 indicates a basic configuration of a linear solid-state image sensor.
A linear solid-state image sensor 10 has a substrate 34 of quartz or some other material which is optically transparent. On this substrate 34 are formed an element array 11 in which photo-responsive elements are disposed linearly, and a drive circuit 12 formed from a thin-film transistor (TFT) provided so as to correspond with each of the photo-responsive elements of the element array 11. The drive circuit 12 has a structure with an analog switch 22 and a shift register 28.
The linear solid-state image sensor 10 scans a wide area at once. Accordingly, it is desirable that the linear solid-state image sensor 10 is as long as possible.
However, from the viewpoint of manufacturing technology, it is difficult to form the element array 11 in a uniform state on the long substrate 34.
Accordingly, in considering the manufacturing yield and the dimensional rating of the currently existing manufacturing apparatus, when a long linear solid-state image sensor 10 is manufactured, it is the best process to connect a plural number of short image sensors in order to create the linear solid-state image sensor 10.
FIG. 2 indicates a conventional solid-state image sensor in which two image sensors are connected.
A first image sensor (hereinafter known as the first chip 34-1) and a second image sensor (hereinafter known as the second chip 34-2) are connected at their end surfaces and in the direction of their length. The first chip 34-1 and second chip 34-2 have a structure whereby a element array 11 and drive circuit 12 are formed on the substrate 34, as indicated in FIG. 1. The surface of the first chip 34-1 and the second chip 34-2 in the vicinity of the connection portion 58 of the first chip 34-1 and second chip 34-2, has pads 36-1a, 36-1b, 36-2a and 362b formed upon it. These pads 36-1a, 36-1b, 36-2a and 36-2b are connected by wires 40 which are bonded.
These wires 40 are the data transfer wires, the power wires and the control signal wires connecting the first chip 34-1 and second chip 34-2.
In addition, the protector glass 38 is provided on the chips 34-1, 34-2.
In a linear solid-state image sensor 10 having a structure such as has been described above, there are also provided in the center, parts for the connection of the pads and wires to the chip. Accordingly, it is necessary to reserve an extra area for the sake of connection to the chip and the extra area necessary creates problems for making the entire sensor more compact.
In addition, when the linear solid-state image sensor 10 is applied to an image processing apparatus 100 such as indicated in FIG. 3, an solid-state image sensor 10 of the completely contact type is used. A protector glass 38 provided on the first chip 34-1 and the second chip 34-2 protects the image sensor from dust and static electricity that is generated by original 102 as it runs between the contact roller 104 and the paper guide 106 of the image processing apparatus 100. In the sensor of the completely contact type, image forming optical system elements are not used and the original 102 is slided on the element array 11 and the image information is directly read by the element array 11. However, in a conventional solid-state image sensor as indicated in FIG. 2, the wire 40 can be damaged by the protector glass 38.